The present invention relates to a plasma processing method and apparatus which can be used for thin-film circuit formation methods in semiconductor and thin-film display industries thin-film circuit formation and, in particular, which allow transistor devices to be formed on such highly insulative substrates as glass, quartz, and compound semiconductors. The present invention also relates to a plasma processing method and apparatus capable of efficiently reducing occurrence of device damage and device breakage that otherwise might occur when a processing-object substrate, which has already been in a charge-stored state since before plasma processing, is subjected to plasma processing in such a charge-stored state.
In recent years, in thin-film device manufacturing fields, there has been a growing demand for process simplification and manufacturing-method modifications toward those which involve less environmental loads, from the viewpoints of manufacturing cost and environmental protection. Thus, there are desires for advancement from conventional engineering methods using chemicals toward engineering methods, as well as apparatuses, in which thin-film processing is performed by applying plasma.
However, such thin-film devices as shown above are manufactured through a wide variety of manufacturing steps, including, for example, a step of heat treatment, a step of water washing treatment, and a step using the plasma application. As a result of this, there are possibilities, at all times, of occurrence of electric charge storage on the top and bottom of the processing-object substrate from various factors.
Thin-film processing and apparatuses using the application of plasma, which include the steps of generating plasma in a vacuum, alienating process gas, and performing processing in combination of physical and chemical reactions by ions and radicals, would involve generation of much larger amounts of charges on the processing-object substrate.
With regard to the charges generated in large amounts, although a dielectric film for insulating metal films is formed as a thin film, involving a threshold value for withstanding voltage in terms of the structure of thin-film circuits, there are cases where if the processing-object substrate is charged and electrified with such charges at which the threshold value would be exceeded, a breakdown of the dielectric film would occur, making it impossible to make up a thin-film circuit. For this reason, it has conventionally been discussed and practiced to use a plasma that would be charged on the processing-object substrate as little as possible, or to reduce the given charges by devising plasma process measures.
Hereinbelow, a typical form of dry etching apparatus is explained with reference to FIG. 3.
Reference numeral 101 denotes a plasma processing vessel for performing a dry etching process, 101a denotes a process gas and inert-gas introducer, 102 denotes an electrode having functions of generating a plasma and serving for placing thereon a processing-object substrate (i.e., a substrate to be processed) 112, 103 denotes an evacuator, 104 denotes a vacuum transfer vessel for putting the processing-object substrate 112 into and out of the plasma processing vessel in a state of vacuum pressure, 104a denotes an evacuator, 104b denotes an inert-gas introducer, 105 denotes a gate door which serves as a partition wall between the plasma processing vessel 101 and the vacuum transfer vessel 104 and which has an opening/closing mechanism, 106 denotes a vacuum conveyance mechanism, 106a denotes a lift pin which is interlocked with the vacuum conveyance mechanism 106 and which operates for placing the processing-object substrate 112 onto the electrode 102, 107 denotes a load lock vessel capable of performing an operation of reducing the internal pressure of the vessel from atmospheric to vacuum state and, conversely, an operation of pressurizing the vessel from vacuum to atmospheric state, 107a denotes an evacuator, 107b denotes an inert-gas introducer, 108 denotes a gate door which serves as a partition wall between the vacuum transfer vessel 104 and the load lock vessel 107 in a vacuum state and which has an opening/closing mechanism, 109 denotes a gate door for holding the load lock vessel 107 in a vacuum state, 110 denotes a substrate storage device in which processing-object substrates 112 are stored, and 111 denotes an atmospheric conveyance mechanism for taking a processing-object substrate 112 out of the substrate storage device 110 and transferring the substrate 112 to the load lock vessel 107.
With respect to the dry etching apparatus constructed as shown above, its operation is explained below.
First, the processing-object substrate 112 (i.e., the substrate to be processed) is taken out of the substrate storage device 110 by the atmospheric conveyance mechanism 111, inert gas is purged from the inert-gas introducer 107b to the load lock vessel 107 to obtain an atmospheric state, the gate door 109 is opened, and the processing-object substrate 112 is transferred to the load lock vessel 107 by the atmospheric conveyance mechanism 111.
Subsequently, the gate door 109 is closed, and in the load lock vessel 107, the operation of the inert-gas introducer 107b is halted and the load lock vessel 107 is evacuated from the evacuator 107a. After the evacuation to a specified pressure is completed, the gate door 108 is opened. The vacuum transfer vessel 104 is normally held in a vacuum state by the evacuator 104a operating for evacuation at all times. The processing-object substrate 112 placed on the load lock vessel 107 is taken out by the vacuum conveyance mechanism 106 and transferred to the vacuum transfer vessel 104, and the gate door 108 is closed.
The evacuator 103 provided at the plasma processing vessel 101 normally performs the evacuation operation, so that the vessel 101 is normally held in the vacuum state. The gate door 105 is opened, and the processing-object substrate 112 present on the vacuum conveyance mechanism 106 within the vacuum transfer vessel 104 is transferred to the electrode 102 of the plasma processing vessel 101. After the processing-object substrate 112 is placed onto the lift pins 106a, the gate door 105 is closed, and the lift pins 106a move down so that the processing-object substrate is placed onto the electrode 102. After that, plasma processing is carried out.
Subsequent to completion of the plasma processing, after performing a process which is a so called charge-neutralizing process by such gas as N2 or O2 and which neutralizes or removes charges electrified on the processing-object substrate 112 by changing the plasma generation area by pressure or power, or during this process, the lift pins 106a move up, so that the processing-object substrate 112 is lifted.
Thereafter, the gate door 105 is opened, and the processing-object substrate 112 present on the lift pins 106a within the plasma processing vessel 101 is taken out of the plasma processing vessel 101 and transferred into the vacuum transfer vessel 104 by the vacuum conveyance mechanism 106.
In this case, the evacuator 103 of the plasma processing vessel 101 performs an evacuation operation so that the reaction product after the plasma processing does not flow into the vacuum transfer vessel 104. The gate door 105 is closed, then the gate door 108 is opened, the processing-object substrate 112 is transferred to the load lock vessel 107 by the vacuum conveyance mechanism 106, and the gate door 108 is closed. The evacuator 107a within the load lock vessel 107 is halted, and the inert gas is purged from the inert-gas introducer 107b, where the interior of the load lock vessel 107 is changed from vacuum pressure to an atmospheric pressure state. Then, the gate door 109 is opened, and the processing-object substrate 112 present in the load lock vessel 107 is taken out and stored into the substrate storage device 110 by the atmospheric conveyance mechanism 111 (see Japanese Unexamined Patent Publication No. 07-106314, and Japanese Patent Nos. 3227812, and 3170849).
However, the processes subsequent to the completion of the plasma processing of the processing-object substrate 112 in the plasma processing vessel 101 include the steps of, after completion of the charge-neutralizing process, opening the gate door 105, taking out the processing-object substrate 112 present on the electrode 102 within the plasma processing vessel 101 from within the plasma processing vessel 101, and then transferring the processing-object substrate 112 into the vacuum transfer vessel 104 by the vacuum conveyance mechanism 106. Thus, potential values of the residual charges remaining on the surface of the processing-object substrate 112 exhibit such behavior as shown in FIG. 4B.
The charges electrified on the surface of the processing-object substrate 112 after the plasma processing show the maximum potential value at the passage through the gate door 105. While still keeping a high voltage state thereafter, the processing-object substrate 112 is placed onto the vacuum transfer vessel 104. There is an issue, in this case, that dielectric breakdown may occur when the charging potential that varies during the transfer of the processing-object substrate 112 in the vacuum has exceeded a withstand voltage threshold 102a of the dielectric film formed on the processing-object substrate 112.
This breakdown is limited to cases where, as shown in FIG. 5, there exists a distance d that satisfies the following formula (Eq. 1) during the transfer of the processing-object substrate 112 in transitions from the charges of +Q at the surface of the electrode 102, as opposed to and polarized from the charges of −Q electrified on the surface of the processing-object substrate 112 (at this time point, the distance d between the rear face of the processing-object substrate 112 and the top surface of the electrode 102 is infinitely large so that the formula (Eq. 1) is not applicable), to the bottom face of the plasma processing vessel, to the bottom face of the gate door 105, and to the bottom face of the vacuum transfer vessel 104:−Q=Cg×Vg=ε×(S/d)×Vg1  (Eq. 1): Basic formula for capacitors,
wherein Cg: capacitor capacity at the gap of distance d, Vg: potential difference at the gap of distance d, S: area, d: distance, ε: dielectric constant. In FIG. 5, Vgmax is a potential at the maximum gap at the distance d.
As can be understood from the above equation (Eq. 1), the reason (for the breakdown) could be attributed to the possibility that Vg may increase upon arrival at a region (dmin) which is affected by d (distance).
Of course, it can easily be presumed that the surface potential of the processing-object substrate 112 increases to its largest level at the moment when the processing-object substrate 112 separates from the electrode 102. At this time point, a portion of the processing-object substrate 112 has passed through the gate door 105, so that even if occurrence of the dielectric breakdown is avoided, the surface potential can abnormally increase only at a portion of the processing-object substrate 112. On this basis, it is inferred that the dielectric breakdown can occur at that portion.
Also, without occurrence of the dielectric breakdown, a thin film bearing an active state, which is generally called damage, formed on the processing-object substrate 112, would cause the composition of the thin film interior to be changed along with local increases in the charges, thus creating a factor for deterioration in characteristics and performance of the thin film.
In common vacuum mass-production equipment, the gate door is manufactured as small as possible in order to reduce the pressure loss upon opening and closing of the gate door. At the point where the processing-object substrate 112 passes through the gate door 105, the distance between the processing-object substrate 112 and the gate door 105 becomes an extremely small one. In other words, the processing-object substrate 112 and the gate door 105 become infinitely close to each other at this point, and the distance d falls within a range subject to influences of the basic formula for electrostatic capacity. The potential Vg in a portion of the processing-object substrate 112 shows a value higher than that on the electrode 102.
In conjunction with the above description, since there are no places where the accumulated charges are discharged as far as the processing-object substrate 112 is transferred in the vacuum, which makes the processing-object substrate 112 keep bearing charges at a very high level until coming to an atmospheric state, portions other than the gate door 105 can become more influenced by the equation (Eq. 1), depending on the configuration of mass-production equipment.
In view of these and other issues of the prior art, an object of the present invention is to provide a plasma processing method and apparatus capable of reducing the amount of charge on a processing-object substrate, which varies during transfer of the processing-object substrate subsequent to its plasma processing.